Line a large cookie sheet with parchment paper and butter heavily.
In a large pot, melt 1 stick of butter and stir until light brown.
Add vanilla extract and stir.
Add all but 2 cups of mini marshmallows and stir until completely melted and smooth.
Add Malt-O-Meal® Crispy Rice cereal and additional 2 cups of mini marshmallows.
Stir until combined.
(Optional) Add desired amount of sprinkles and fold in until combined.
Pour Malt-O-Meal® Crispy Rice cereal mixture onto cookie sheet and gently press with damp hands to spread out evenly.
(Optional) Add additional sprinkles on top of spread out mixture.
Cut and store in a covered container and enjoy!